In its simplest form a ceramic capacitor consists of a relatively thin wafer of desired shape and size formed by firing a ceramic dielectric composition, the wafer having electrodes on the opposite faces thereof. In many cases, however, it is desired to use a capacitor having a plurality of such wafers alternating with conductive layers, alternate ones of said conductive layers being exposed at the same edge faces of the capacitor and electrically joined there, for example by a termination electrode.
In a typical known method for producing such ceramic capacitors, an electroding paste of a noble metal such as platinum or palladium is applied to the top face of a small, usually cast, thin sheet of a suitable ceramic dielectric composition bonded with an organic temporary binder, the application being made in such manner that the deposit of electroding paste extends to one edge of the sheet only and a clear margin is left around three sides of the deposit. A plurality of the small sheets thus coated with electrode paste are then stacked, successive sheets being rotated about an axis normal to the plane of the sheet, whereby successive electroding paste deposits extend to opposite edges of the stack. The stack of paste-coated sheets is then suitably consolidated and heated to drive off or decompose the organic binders of the ceramic sheet and the electroding paste and to sinter the dielectric composition into a unitary, multilayer body having successive electrodes exposed on opposite ends thereof. The electrodes exposed on each end are then electrically connected with a termination electrode in known manner.
Because of the necessity for using noble metal internal electrodes in the process just described, monolithic ceramic capacitors are expensive. Lower cost, silver electrodes such as are commonly used with other ceramic capacitors are generally unsuitable for monolithic capacitors because the silver, applied as an electrode paste, would be subjected to a high temperature during firing to mature the ceramic and would thereby be deleteriously affected. Accordingly, a method of producing monolithic capacitors that does not require the use of noble or very expensive metals has been desired.
Such a method has been described in U.S. Pat. No. 3,679,950, granted July 25, 1972. In that patent a number of procedures are disclosed which involve the formation of sintered ceramic matrices that have strata of dense dielectric material alternating with strata of porous ceramic material and the subsequent deposition of conductive material, which may be low-cost metals, in said porous strata.
While very satisfactory, relatively inexpensive, monolithic capacitors have been made by methods disclosed in the above-mentioned patent, maintaining continuity of metal in the internal electrodes has been found to be a problem at times. It is also desirable, particularly when producing capacitors for use at high frequency, to keep the electrode resistance as low as possible.
Accordingly, it is an object of the present invention to provide an improvement on the procedures disclosed in the above-mentioned patent which will result in the production of sintered ceramic matrices in which internal electrodes can be formed by introduction of conductive material, such as metal, to form capacitors wherein continuity of and low resistance in such electrodes is easily obtained, while the ceramic matrix prior to impregnation has adequate strength.